import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 28779
 * Date: 2023-11-22
 * Time: 18:36
 */

//回显服务器
//客户端发的请求是啥，服务器返回的响应就是啥
public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }
    public void start() throws IOException {
        System.out.println("服务器启动！");
        while(true) {
            // 1.读取数据，并请求
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            //  转换成字符转
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            // 2.根据请求，计算出响应
            String response = process(request);
            // 3.把响应写回给客户端
            //   此时需要告知网卡，要发的内容是啥，要发给谁
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //记录日记，方便观察程序执行效果
            System.out.printf("[%s:%d] req: %s , resp: %s\n", responsePacket.getAddress().toString(), responsePacket.getPort(),
                    request, response);
        }
    }

    //根据请求计算响应，由于是回显程序，响应内容和请求完全一样
    private String process(String request) {
        return request;
    }
    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}